This was from a Submission Only event held by US Grappling in Virginia, November 2011.
I'm in the Blue Gi, Blue belt division, Under 149 lb's:
I cross grip for my lapel grip then as I establish my sleeve grip, I begin circling to my right, which forces my opponent to follow as he begins to search for his grips.
**** By "cross grip" I mean that I reach for his lapel with my rear hand. In Judo, we rarely reach for the lapel we desire with the lead hand as this can lead to your being on the receiving end of a footsweep. I've actually footswept guys in NoGi divisions as they reach in to tie up with me. It really does happen.****
At :17 I feel him circle into me and his posture feels weak, so use my lapel grip to reach over his back and set up a stronger, more powerful/dominating grip and begin to bend him over/kill his posture even further.
At this point, you'll notice how wide his feet are (wider than shoulder with), they are square (on the same line/plane), and he is sitting back on his hills/butt sticking out, head forward of his waist and feet. This is the ideal posture for your opponent to set up an uchimata (and ouchi gari, kouchi gari et cetera).
He than makes the fatal mistake and steps back behind what will be my reaping/lifting leg for the uchimata with HIS left foot. The rest is pretty basic:
I land in half-guard and from learning the hard way in earlier matches, immediately pummel/lace my power grip right hand back inside to hunt for the underhook on the far side (otherwise he takes my back). He beats me to it, I lose the underhook race, and I settle for bringing my elbow down to kill his underhook ("escrima" they would yell at me in Brazil).
My opponent lets me keep him pretty flat on his back despite having the underhook and his weak/lazy underhook is what sets up the D'Arce. His head is bent down and his spine curved, letting me slowly tighten up my D'Arce grip.
Unlike the way some people do it, I like to lock the D'Arce and step over into mount making it a slightly different kind of squeeze. I've been told it feels closer to a guillotine than the way the D'Arce normally feels (to me it normally feels like scissors clamping down on my neck).
At any rate, here's an example of how some basic, fundamental of Judo: cross grip, circle away, and when the opponent follows you establish a power/high/dominating grip, and take advantage of poor posture and defensive stance to land on top, score points, and begin to pass the guard.